const func1 = (x) => x;
const func2 = (x) => {
  x;
};
const func3 = (x) => ({ x });
//问以下打印的结果
console.log(func1(1)); //1
console.log(func2(1)); //undefined
console.log(func3(1)); //{x:1}

//箭头函数写成 () => 表达式时，会隐式返回该表达式的值
